The present invention relates generally to stage lighting instruments having associated color-changing mechanisms and particularly to a light source including plural, serial lens elements and selected-wavelength modifiers that are adjustable in the plane of the modifier.
Stage lighting instruments having motorized subsytems operated by remote-control means are commonly referred to as xe2x80x9cmoving lightsxe2x80x9d or xe2x80x9cautomated luminaires.xe2x80x9d Among these are two general varieties: spot luminaires and wash luminaires. Spot luminaires are similar to the xe2x80x9cprofile spotxe2x80x9d or ellipsoidal reflector spotlight commonly used in theaters, and provide a hard-edged beam of light. This kind of spotlight has a gate aperture at which various devices can be placed to define the shape or profile of the light beam and has a projection optical system including one or more objective lens elements. A spot luminaire projects an image of the brightly-illuminated gate aperture, including whatever light-shaping, pattern-generating, or image-forming devices might be placed there. Wash luminaires are similar to the xe2x80x9cFresnel spotxe2x80x9d luminaire, which provides a soft-edged, ill-defined beam that can be varied in size by moving the lamp and reflector towards or away from the lens. This kind of wash light has no gate aperture and projects no image, but projects only a soft-edged pool of light shaped by whatever lens or lenses are mounted over the exit aperture of the luminaire.
Color filter systems for automated spot luminaires take advantage of a region near the gate aperture where the diameter of the light beam is small, typically at or near a second focal point of an ellipsoidal reflector, the lamp being located at the first focal point. As in U.S. Pat. Nos. 4,392,187 and 4,800,474 to Bornhorst, small dichroic color filters are mounted on wheels and exchanged in combination to impart a wide variety of vibrant colors to the light beam. The colors are changed step-wise, instantly changing from one color to another.
Color filter systems for automated wash luminaires take advantage of a certain property of dichroic filters to create smoothly changing colors or color cross-fades. As in U.S. Pat. Nos. 4,392,187; 4,602,321; and 5,073,847 to Bornhorst, pivoting dichroic filters vary the angle of incidence of the light beam upon the filter to vary the hue and saturation of color in a continuous fashion. These color filter systems occupy a considerable volume within the luminaire and are not readily adaptable to spot luminaires.
A spot luminaire having a fully cross-fadeable color mixing system that projects a smooth and uniformly-colored beam of light has long been the goal of many lighting manufacturers. Leclerq describes the problem succinctly in U.S. Pat. No. 4,745,531 with respect to traditional gelatin or plastic xe2x80x98gelxe2x80x99 color filters, which are normally placed over the exit aperture of a luminaire downstream of all lens elements. When such a color filter partly intercepts the light beam of a spotlight, only part of the beam is coloredxe2x80x94that part of the beam which passes through the filter. The spot of light is then partly colored and partly white. It is desirable to have homogeneous mixing of the colored light and the white light at the projected spot of light. Although Leclerq discloses a color filter apparatus that purports to accomplish this, it is not discernable from the disclosure how this is accomplished.
U.S. Pat. No. 4,894,760 to Callahan, discloses a color-mixing light fixture employing a single, movable, multi-filter array that varies the apparent color of a light beam by additively mixing varying proportions of differently colored light. Callahan attempts to achieve the desired homogeneous mixing of differently colored light by locating the filter array at a xe2x80x9chyperfocal regionxe2x80x9d between two lens elements, a location in the optical path at which light rays passing through a given point in a plane intersecting the light beam are uniformly distributed across the beam where it illuminates an object. This approach theoretically yields some integration of colors, but experiments have shown that real-world limitations make this a less-than-ideal solution to the problem. For example, the theoretical plane of the xe2x80x9chyperfocal regionxe2x80x9d has negligible depth along the optical axis of the system thereby making correct location of a co-planar array of color filters very critical. As the filter array moves away from this theoretical plane, the color integration degrades rapidly. Further, real-world limitations of lens design frequently yield aberrations such as field curvature which make the theoretical plane of the xe2x80x9chyperfocal regionxe2x80x9d non-planar, and thus impossible to use effectively with planar filter elements. Using such a hyperfocal region would require a non-planar filter array precisely placed in a domain of non-planar movement.
U.S. Pat. No. 5,188,452 to Ryan, discloses a color mixing lighting assembly for a spot luminaire including a light source, a color filter set, an objective lens set, and a color mixing channel located between the color filters and the objective lens set. The color mixing channel is a highly-polished, hollow tube of hexagonal or other cross-section having a reflective interior surface. The tube is made of specific diametric and longitudinal dimensions to accomplish color mixing or integration of various primary colors of light. This tubular apparatus is positioned upstream of the aperture gate and necessarily adds length to the overall optical system. The use of such length is frequently preferred for other purposes, such as for zoom optics.
U.S. Pat. No. 5,790,329 to Klaus et al, discloses a color changing device for illumination purposes that provides continuously variable light color using a subtractive color mixing method. Dichroic color filters are introduced into the light path of a spotlight at a place between objective lenses where the illumination field of the lamp is imaged. The image of the light source tends to be relatively large at this location because the diameter of the light beam is large compared to the diameter of the light beam closer to the light source itself, for example; at the aperture gate. This requires that the color filters be large enough to cover the entire beam, which makes for added expense since dichroic filters are themselves rather expensive. Further, experiments have shown that at certain positions of the filtersxe2x80x94particularly at around 90% coveragexe2x80x94the color integration is noticeably non-homogeneous with particular distributions of unfiltered white light diluting the saturation of the colored beam over a certain part of the beam. This creates a noticeable, non-homogeneous color effect in a range between fill saturation and pastel shades of color, which is distracting to view and therefore undesirable.
Other techniques disclosed in U.S. Pat. No. 4,914,556 to Richardson; U.S. Pat. No. 5,282,121 to Bornhorst et al; U.S. Pat. No. 5,426,576 to Hewlett; U.S. Pat. No. 5,515,254 to Smith; and U.S. Pat. No. 5,829,868 to Bornhorst et al; require complex patterning of the filter material, continuously-variable hue characteristic filter material, or both. These types of filters are expensive to fabricate and contribute to the high cost of manufacturing an automated luminaire having an associated color changing mechanism.
It is an object of the invention to provide a simple, cost-efficient color mixing system that projects a smooth and uniformly colored beam of light.
In accordance with one aspect of the present invention, a stage lighting instrument having a high-intensity light source or lamp coupled with a concave reflector, and a projection optical system, further includes a color filter and dimming system located within a lens system that includes a well-defined aperture stop, and forms a real image of the light source near the aperture stop so that the color filter and dimming apparatus occupies a volume of space near the aperture stop and within the real image of the light source. By locating the color and dimming apparatus near the aperture stop and within the volume occupied by a real image of the light source, superior color mixing, dimming and integration is achieved using simple, unpatterned filters and a simply-shaped dimmer panel.
In accordance with another aspect of the present invention, a stage lighting instrument having a high-intensity light source or lamp coupled with a concave reflector, and a projection lens system having a well-defined aperture stop, forms a real image of the light source near the aperture stop, and further includes a color filter system located adjacent the light source so that a real image of the color filter system is formed co-extensively with the real image of the light source at the aperture stop. This is equivalent to locating the color filter system in the volume occupied by the real image of the light source as formed at the aperture stop.
In accordance with a further aspect of the invention, diffusion glass elements included in the color filter system effectively transform spotlight performance into wash-light performance in a continuously-variable manner.